A ball grid array (BGA) is related to a pin grid array (PGA), in which an integrated circuit (IC) package includes face covered or partly covered with pins in a PGA or balls in a BGA, usually in a grid or matrix pattern. The pins and balls conduct electrical signals from the IC positioned in the IC package to a printed circuit board (PCB) e.g., a printed wiring board, on which the package is placed. In a BGA, the balls are conductive balls, typically formed from solder and positioned at the bottom of the IC package. Usually the PCB carries copper pads in a matrix pattern that matches the matrix pattern formed by the conductive balls. In some manufacturing techniques, the assembly is heated in a reflow oven or infrared heater, causing the conductive balls to stick to the PCB. Usually, the composition of the solder alloy and soldering temperature are chosen such that the solder does not completely melt, but stays semi-liquid, allowing each conductive ball to stay separate from its neighbors.
A BGA IC package usually has a lower thermal resistance between the IC package the PCB such that any heat generated by the IC flows more easily to the PCB, preventing the IC chip from overheating. Also, because the conductive balls of a BGA are shorter than pins of a PGA as an electrical conductor, the balls have lower inductance than the pins and prevent unwanted distortion of signals in high-speed electronic circuits. One disadvantage of a BGA, however, is that the conductive balls often cannot flex in the manner of pins in a PGA. Any bending and thermal expansion within the PCB is transmitted directly to the BGA IC package, causing solder joints to fracture under high thermal or mechanical stresses. In some designs, this is overcome by matching the coefficient of thermal expansion (CTE) between the PCB and IC package, but even then, it is difficult to inspect for soldering failure once the IC package is secured to a PCB.
As a result, a BGA package has limited inspectability, reworkability and testability and has reliability issues and design limitations when the CTE mismatch between the IC package and the PCB is large. There are a number of proposals with different BGA products, but these products increase the package footprint, height, weight and assembly steps more than desired.